Mobile communication method and mobile communication apparatus

ABSTRACT

A mobile communication apparatus includes a registration request part ( 47 ) requesting a correspondent node to make location registration, a BU list memory ( 45 ) keeping a list of the correspondent nodes which have made the location registration, a handover detection part ( 41 ) detecting the start of a handover, and a registration cancellation processing part ( 46 ) canceling the location registration of the correspondent nodes in the BU list, upon notification of start of handover by the handover detection part ( 41 ), thereby reducing loss of packets transmitted from the correspondent nodes during the handover, because the route optimization applied to the correspondent nodes registered in the BU list at the start of the handover is canceled by requesting the cancellation to the correspondent nodes.

This application is a U.S. National Phase Application of PCTInternational Application PCT/JP2004/016702 dated Nov. 4, 2004.

TECHNICAL FIELD

This invention relates to a mobile communication method and a mobilecommunication apparatus using an internet protocol.

BACKGROUND ART

As a conventional mobile communication method using an internetprotocol, the one using Mobile IPv6 which is disclosed in “MobilitySupport in IPv6”, IETF RFC3775 written by David B. Johnson et al. isknown.

The operation of the conventional Mobile IPv6 will be explained withreference to a sequence diagram of FIG. 7. Note that black circles inthe drawing indicate routing nodes.

First of all, a mobile communication apparatus MN holds a home address(hereinafter, referred to as HoA) which will not change with movement,and is connected to an access router (hereinafter, referred to as OAR).It receives data packets from a correspondent node (hereinafter,referred to as CN) through the OAR (step S700).

The mobile communication apparatus moves to another access router(hereinafter, referred to as NAR) from this state, and generates acare-of address (hereinafter, referred to as CoA) based on a subnetprefix included in a router advertisement (hereinafter, referred to asRA) message (step S701) received from the NAR after a handover in a datalink layer is finished (step S702).

Next, the mobile communication apparatus MN sends a binding update(hereinafter, referred to as BU) message including HoA and CoA to a homeagent HA (step S703).

The home agent HA, after receiving the BU message from the mobilecommunication apparatus MN, in the case that there exists an entry whichcorresponds to the HoA included in the received BU message in a bindingcache stored by the home agent HA itself, updates the entry. In the casethat there does not exist a corresponding entry, a new entry isgenerated. After that, the home agent HA sends to the mobilecommunication apparatus MN a binding acknowledgement (hereinafter,referred to as BA) message indicating that a registration is completed(step S704).

Next, the mobile communication apparatus MN confirms that theregistration is completed by receiving the BA message. According to theabove, packets sent addressed to the HoA of the mobile communicationapparatus MN are intercepted by the home agent HA and tunneled to theCoA of the mobile communication apparatus MN.

However, in these standard operations of Mobile IPv6, all packetsaddressed to the HoA of the mobile communication apparatus MN are routedvia the home agent HA; therefore, the route will be redundant.

Therefore, in Mobile IPv6, a route optimization procedure which allowspackets to be directly transmitted to the mobile communication apparatusMN without routing via the home agent HA is prescribed as an optionalfeature. In the route optimization procedure, the mobile communicationapparatus MN, after the registration to the home agent HA as thestandard operation has been completed, sends the BU message includingthe HoA and CoA to the correspondent node CN with which the apparatuscurrently communicates (step S706). Or, when a received packet istunneled by the home agent HA, the BU message including HoA and CoA issent to the correspondent node CN which is the transmission origin andis the node with which communication is to be made.

Next, the correspondent node CN which has received the BU message fromthe mobile communication apparatus MN updates or generates the entryconcerning the HoA of the mobile communication apparatus MN in thebinding cache in the same way as the home agent HA. In the case ofperforming a registration processing to the correspondent node CN, aprocedure for securing security (step S705) might be performed.

According to the above operation, the correspondent node CN can forwarda packet directly to the mobile communication apparatus MN withoutsending the packet to the corresponding care-of address and thus beingrouted via the home agent HA, because there exists a destination addressof the transmission packet in the binding cache (step S707).

According to the route optimization procedure, packet transmission delaycan be made small, which is effective when performing close-to-real-timecommunication. For example, when an application to be used requires thereal-time communication, there is a method of decreasing the packetdelay by executing the route optimization procedure as disclosed inJP-A-2001-144811.

However, in the conventional structure, when the mobile communicationapparatus moves to another access router while communicating with thecorrespondent node with the route optimization performed, the apparatusstarts a location registration to the correspondent node after thelocation registration with respect to the home agent has been completed,and therefore, packets transmitted to the care-of address of the mobilecommunication apparatus during the registration are transmitted to thecare-of address before the movement, so that there is a problem thatpacket loss occurs.

DISCLOSURE OF THE INVENTION

An object of the invention is to provide a mobile communicationapparatus which reduces packet loss during a handover.

A mobile communication method of the invention includes a step that amobile communication apparatus performs a location registration to ahome agent managing the movement of the mobile communication apparatusthrough an access router connecting to the same sub-network, a step thatthe mobile communication apparatus performs the location registration toa correspondent node connected to different sub-network, a step that themobile communication apparatus directly performs communication with thecorrespondent node, a step that the mobile communication apparatusdetects the start of handover, and a step that the mobile communicationapparatus instructs the cancellation of location registration to thecorrespondent node on receipt of the detection of the start of thehandover. According to the steps, packets transmitted from thecorrespondent node are routed via the home agent, and when the mobilecommunication apparatus is performing the location registration, packetstransmitted from the correspondent node to the home agent begin to beforwarded to the new location of the mobile communication apparatus, andtherefore, packet loss at the time of handover can be reduced.

A mobile communication apparatus of the invention keeps a list in whichaddresses and other information of the correspondent nodes to which alocation registration request has been performed in the past areentered, and gives notice of the cancellation of location registrationto all correspondent nodes written in the list. Accordingly, packet lossof packets transmitted from all correspondent nodes can be reduced.

Further, the mobile communication apparatus of the invention keeps alist in which addresses and other information of the correspondent nodesto which the location registration request has been performed in thepast are entered, and gives notice of the cancellation of locationregistration to those correspondent nodes written in the list whichsatisfy a prescribed condition. Accordingly, the registrationcancellation processing is performed only to the correspondent nodeswhich satisfy the prescribed condition, and therefore the increase oftraffic caused by registration cancellation messages is suppressed.

Further, the mobile communication apparatus of the invention keeps thelist in which addresses and other information of the correspondent nodesto which the location registration request have been performed in thepast are entered, sets a flag ordering the transmission of theregistration cancellation message of the correspondent nodes whichsatisfy the prescribed condition in the entries of those correspondentnodes written in the list, and transmits the registration cancellationmessage to the correspondent nodes to which the flag is set.Accordingly, the mobile communication apparatus can determine where totransmit the registration cancellation message by referring to theflags.

A prescribed condition for selecting correspondent nodes in theinvention is that the frequency of communication between the mobilecommunication apparatus and the correspondent node is high. Accordingly,packet loss from a correspondent node having high frequency ofcommunication with the mobile communication apparatus can be reduced.

Another prescribed condition for selecting correspondent nodes in themobile communication method according to the invention is that a sessionis established between the mobile communication apparatus and thecorrespondent node. Accordingly, a disconnection of the session with thecorrespondent node caused by packet loss can be prevented.

Still another prescribed condition for selecting correspondent nodes inthe mobile communication, method according to the invention is that anapplication using communication between the mobile communicationapparatus and the correspondent node is inoperable when there is packetloss. Accordingly, an application that is inoperable when there ispacket loss is usable even at the time of handover.

In the mobile communication method according to the invention, themobile communication apparatus keeps the list in which addresses andother information of the correspondent nodes to which the locationregistration request has performed in the past are entered, and notifiesthe cancellation of location registration to correspondent nodes writtenin the list in the order of high priority. Accordingly, when there isinsufficient time for sending the registration cancellation message toall correspondent nodes there is a good possibility that theregistration cancellation processing can be performed to thecorrespondent nodes whose priority is high.

The priority in the correspondent nodes in the mobile communicationmethod according to the invention is given to those with high frequencyof communication with the mobile communication apparatus. Accordingly,packet loss from the correspondent nodes having high frequency ofcommunication with the mobile communication apparatus can be reduced.

The mobile communication apparatus in the mobile communication methodaccording to the invention further includes a step of giving priority tothe correspondent nodes whose location registration in the list entryhas not yet been cancelled, and giving the location registration requestto such correspondent nodes after moving to a different subnetwork.Accordingly, packet loss from the correspondent nodes to which theregistration cancellation message was not sent can be reduced.

A mobile communication apparatus of the invention includes aregistration request part requesting a correspondent node to make alocation registration, a list storage part keeping a list of thecorrespondent nodes to which the location registration has beenperformed, a handover detection part detecting the start of a handoverand a registration cancellation processing part performing thecancellation of location registration of the correspondent nodes in thelist upon notification from the handover detection part. Accordingly,the mobile communication apparatus can know the correspondent nodes towhich a registration cancellation message should be sent by referringthe list.

In addition, the list of the mobile communication apparatus according tothe invention is the one in which registration cancellation informationis added to a binding update list. Accordingly, it is not necessary thatthe mobile communication apparatus make and keep a new list.

The mobile communication apparatus of the invention further includespriority information indicating the order in which the registrationcancellation shall be performed. Accordingly, the mobile communicationapparatus can easily know the priority.

Further, in the mobile communication apparatus of the invention, thecorrespondent nodes are listed in the order of high priority.Accordingly, the mobile communication apparatus can know the prioritywithout keeping a category field in the list indicating priority.

The cancellation of location registration in the mobile communicationapparatus according to the invention is performed in the order of highfrequency of communication between the mobile communication apparatusand the correspondent node. Accordingly, the registration cancellationprocessing can be performed first for those nodes with high possibilityof packet loss, and therefore packet loss can be reduced efficiently.

The cancellation of location registration in the mobile communicationapparatus according to the invention is performed giving priority tocorrespondent nodes where a session has been established with the mobilecommunication apparatus. Accordingly, the registration cancellationprocessing can be performed first for those nodes with high possibilitythat the session will be disconnected due to the occurrence of packetloss, and therefore packet loss can be reduced efficiently.

The cancellation of location registration in the mobile communicationapparatus according to the invention is performed in the case that anapplication using communication between the mobile communicationapparatus and the correspondent node is inoperable when there is packetloss. Accordingly, the registration cancellation processing can beperformed first for the applications that would suffer greatinconvenience by the occurrence of packet loss, and therefore packetloss can be reduced efficiently.

The mobile communication method according to the invention furtherincludes a step of determining whether the connected access routerperforms handover processing using a fast mobile IP or not, and in thecase it is determined that handover processing using the fast mobile IPis performed, the request for cancellation of location registration isnot given to the communication nodes which have performed locationregistration in the past. Accordingly, unnecessary processing, whichperforms the registration cancellation of communication nodes eventhough packet loss will not occur because the fast mobile IP is applied,can be avoided.

The mobile communication apparatus according to the invention furtherincludes a fast mobile IP detection part detecting that a connectingaccess router performs handover processing using a fast mobile IP, andwhen the fast mobile IP detection part detects the performance of thefast mobile IP, the detection part instructs the registrationcancellation processing part not to request the communication nodes tocancel location registration. Accordingly, unnecessary processing, whichperforms the registration cancellation of the communication nodes eventhough packet loss will not occur because the fast mobile IP is applied,can be avoided.

As described above, according to the invention, packet loss occurringwhen the handover is performed by a mobile communication apparatus inthe route optimization state can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration view of a mobile communication systemaccording to Embodiment 1 of the invention;

FIG. 2 is a configuration diagram of a mobile communication apparatusaccording to Embodiment 1 of the invention;

FIG. 3 is a flow chart showing an operation of the mobile communicationapparatus according to Embodiment 1 of the invention;

FIG. 4 is a configuration chart of a binding-update list according toEmbodiment 1 and Embodiment 2 of the invention;

FIG. 5 is a sequence diagram showing an operation of the mobilecommunication system according to Embodiment 1 of the invention;

FIG. 6 is a chart showing a format of a binding-update message accordingto Embodiment 1 of the invention; and

FIG. 7 is a diagram showing a sequence according to a conventionalmobile IP.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the invention will be explained withreference to the drawings.

EMBODIMENT 1

FIG. 1 is a configuration view of a mobile communication systemaccording to Embodiment 1 of the invention. In FIG. 1, Internet 10includes a plurality of routers forwarding packets using an Internetprotocol, a mobile communication apparatus MN11 includes not less thanone wireless interface or not less than one wired interface, and acorrespondent node CN12 communicates with the mobile communicationapparatus 11. A home agent HA13 performs location management of themobile communication apparatus 11, access routers AR14 to 17 areconnected to the Internet with a wireless interface or a wiredinterface. Here, a configuration diagram of the mobile communicationapparatus MN11 is shown in FIG. 2.

In FIG. 2, the mobile communication apparatus 11 includes a lower layerprocessing part 41 performing the lower layer processing such asmodulation, demodulation and access control, an IP processing part 42performing an IP layer processing, an upper layer processing part 43performing a session management and application control, a registrationcancellation processing part 46 receiving a trigger from the lower layerprocessing part and starting a registration cancellation processing, anda registration request part 47 requesting the correspondent node 12 orthe home agent to register a location. Further, the IP processing part42 has a mobile IP processing part 44 performing a processing of amobile IP and a BU list memory 45 storing a binding update (BU) list inwhich addresses and other information of nodes to which BU messages havebeen sent are written. In FIG. 2, the registration cancellationprocessing part 46 and the registration request part 47 are separatedfrom the IP processing part 42, but these parts may be included in theIP processing part 42. Additionally, the lower layer processing part 41includes a handover detection part, and the BU list memory 45corresponds to a list storage part.

A configuration of the BU list is shown in FIG. 4.

In FIG. 4, the BU list includes the transmission destination address ofthe BU message 1101, the home address set in the BU message 1102, thecare-of address set in the BU message 1103, the sequence number of theBU message 1104, a registration cancellation processing flag 1105indicating whether the registration cancellation processing shall beperformed or not, a priority degree 1106 indicating a degree of priorityof -performing the registration cancellation processing, and the like.

The registration cancellation processing flag 1105 is set by the mobilecommunication node MN11, based on the communication status with thecorrespondent nodes included in the BU list 45. For example, when a TCPsession is started with the correspondent node, the registrationcancellation processing flag 1105 is set to ON, and when the TCP sessionis completed, it is set to OFF. It is also possible that theregistration cancellation processing flag 1105 is set based on thefrequency of communication with the correspondent nodes in the past. Forexample, in the case that the frequency of communication is high, theregistration cancellation processing flag is set. Further, it ispossible that the registration cancellation processing flag 1105 is setbased on the kind of application used with the correspondent nodes inthe past. For example, in the case of using the application that isinoperable when there is packet loss such as a file forwarding, theregistration cancellation processing flag 1105 is set so as to performthe registration cancellation processing. Further, when the accessrouter before movement and the access router at the movement destinationsupport a fast mobile IP (indicated in “Fast Handovers for Mobile IPv6”,an Internet draft under preparation by IETF), the registrationcancellation processing flag 1105 is set to OFF. This is because packetloss does not occur when the fast mobile IP is applied and there is nonecessity of performing the registration cancellation. Here, whether theaccess router apparatus of the movement origin supports the fast mobileIP or not can be determined by the value of a code field in a handovercapability option added to a router advertisement message. Or, in thecase that there is no response to a proxy router solicitation messagetransmitted by the mobile communication apparatus, it can be determinedthat the access router apparatus of the movement origin does not supportthe fast mobile IP. Additionally, the flag can be set in considerationof plural conditions. Note that a fast mobile IP detection partaccording to the invention is included in the mobile IP processing part44, and instructs the registration request part 47 not to requirecorresponding communication nodes to cancel registration by changing theregistration cancellation processing flag 1105 of the BU list memory 45to be OFF.

The priority 1106 is set based on the status of communication withrespective correspondent nodes included in the BU list 45. For example,the priority 1106 of a correspondent node is set higher where there ishigher frequency of communication with that correspondent node.

The operation and effect of the mobile communication apparatus 11constituted as above will be explained as follows.

FIG. 3 is a flow chart showing the operation of the mobile communicationapparatus when a handover takes place.

First, the lower layer processing part 41 checks whether a L2 triggerhas been detected (step S501). In the case that the lower layerprocessing part 41 is “IEEE802.11”, a beacon signal is used for thetrigger.

When the L2 trigger is detected from an AR 15, the mobile IP processingpart 44 determines that the access router AR15 shall be the handoverdestination. Then, the registration cancellation processing part 46refers to the stored BU list 45 and performs the registrationcancellation processing with respect to the correspondent node CN12whose entry exists in the BU list 45. In short, the registrationcancellation processing part 46 determines whether there is a CN towhich route optimization is applied or not in the BU list 45 (stepS502), and if there is no such CN, operation proceeds to step S504.

On the other hand, when there is a CN to which route optimization isapplied, the mobile IP processing part 44 sends a BU message whichincludes the home address HoA of the mobile communication apparatus 11itself and the current care-of address CoA1 and in which the lifetimefield is set to “0”, to the correspondent nodes in which theregistration cancellation processing flag 1105 is ON, according to thepriority order 1106 (step S503). The BU message is shown in FIG. 6. Alifetime field 61 indicates the valid period in which the mobilecommunication apparatus 11 which has sent the BU message can directlycommunicate with the correspondent node 12 of the transmissiondestination using the current care-of address. The indication of “0” ofthe lifetime field 61 means that the mobile communication apparatus 11makes the direct communication with the correspondent node 12 using thecurrent care-of address invalid.

Next, the lower layer processing part 41 performs the handover in thelower layer (step S504).

Next, the mobile IP processing part 44 receives a RA message from theAR15, and generates a care-of address CoA2 from a subnet prefix includedin the RA message (step S505).

Next, the mobile IP processing part 44 sends the BU message includingthe home address HoA of the mobile communication apparatus 11 itself andthe care-of address CoA2 to a home agent HA13 (step S506).

The above is the operation when the handover is detected at the time ofmovement performed by the mobile communication apparatus 11. It is alsopossible that another list in which address of the correspondent node iscombined with the registration cancellation processing flag, and thepriority order is stored and referred to instead of the BU listcomprising the registration cancellation processing flag and thepriority order. Or, it is effective that correspondent nodes are listedin the order of high priority in the BU list, and the registrationcanceling processing is performed in accordance with this order.

Note that the above registration cancellation processing flag and thepriority order are not essential features, and it is also possible thatthe registration cancellation processing can be performed on all thecorrespondent nodes registered in the BU list.

Next, the operation when the handover takes place in the mobilecommunication system of the embodiment will be explained with referenceto the sequence diagram of FIG. 5. The operation up until the mobilecommunication apparatus 11 is connected to an AR14 and performs theroute optimization with the correspondent node 12 is same as theconventional example shown in FIG. 7; namely, data packets addressed tothe mobile communication apparatus 11 from the correspondent node 12 aredirectly transmitted to the mobile communication apparatus MN11 throughthe AR14 (step S800).

First, the mobile communication apparatus MN11 moves, and detects atrigger from an access router AR15 different from the currentlyconnected access router 14 (step S801), and determines the access routerAR15 to be the handover destination. The mobile communication apparatusMN11 performs the registration cancellation processing, and sends the BUmessage to the correspondent node CN12 (step S802). The correspondentnode CN12, after receiving the BU message from the mobile communicationapparatus MN11, checks whether the lifetime field 61 is set to “0”. Inthe case that the lifetime field 61 is set to “0”, the correspondentnode CN12 cancels the entry in the keeping binding cache whose homeaddress matches the home address HoA of the mobile communicationapparatus MN11. In the case that the lifetime field 61 is not “0”, thecorrespondent node CN12 performs a normal registration processing. Theseprocessings of the correspondent node CN12 are standard mobile IPprocessings.

After that, packets transmitted from the correspondent node CN12 andaddressed to the mobile communication apparatus MN11 are transmitted andaddressed to the home address HoA of the mobile communication apparatusMN11. The home agent HA13 intercepts the packets transmitted andaddressed to the home address HoA of the mobile communication apparatusMN11, and tunnels them to a care-of address CoA1 managed by the formerrouter AR14 (step S803), in the mobile communication apparatus MN11.

Then, the mobile communication apparatus MN11 performs the handover inthe lower layer and receives the RA message from the AR15 (step S804).The mobile communication apparatus MN11 generates a care-of address CoA2based on the subnet prefix included in the RA message (step S805).

After that, the mobile communication apparatus MN11 sends a BU messageincluding its home address HoA and the care-of address CoA2 to the homeagent HA13 (step S806).

The home agent HA13, after receiving the BU message, generates orupdates the entry associating the home address HoA of the mobilecommunication apparatus MN11 with the care-of address CoA2. Then, thehome agent HA13 sends a BA message addressed to the mobile communicationapparatus MN11 (step S807) The mobile communication apparatus NM11verifies that the registration is completed by receiving the BA messagefrom the home agent HA13.

After that, packets addressed to the home address HoA of the mobilecommunication apparatus MN11 are intercepted by the home agent HA andforwarded to the new care-of address CoA2 of the mobile communicationapparatus MN11 (step S808).

After that, the mobile communication apparatus MN11 sends a BU messageincluding its home address HoA and the care-of address CoA2 to thecorrespondent node CN12 (step S809). Note that there is a case where themobile communication apparatus MN11 performs a procedure for security onthe correspondent node CN12 before sending the BU message to thecorrespondent node CN12 (step S810).

When there are plural entries in the BU list 45 stored by the mobilecommunication apparatus NM11, the registration cancellation processingis performed on all entries in the same way. In addition, it is alsopossible that the security procedure in the step S810 and thetransmission of the BU message in the step S809 are omitted and allpackets are transmitted and received via the home agent.

As described above, in the embodiment, the registration cancellationprocessing part 46 of the mobile communication apparatus 11 determineswhether the route optimization has been applied to the correspondentnode 12 registered in the BU list or not, and in the case that the routeoptimization has been applied, the route optimization is cancelledbefore performing the handover processing. Accordingly, all data packetsto the mobile communication apparatus 11 from the correspondent node 12are routed via the home agent, therefore, it can be prevented that whilethe mobile communication apparatus 11 is changing the care-of addressand notifying the address to the home agent, a data packet addressed tothe mobile communication apparatus is directly delivered to the care-ofaddress before movement so that the packet is lost.

The registration cancellation processing is performed on the nodes wherecommunication frequency with the mobile communication apparatus is high,and therefore the loss of packets from the correspondent nodes withwhich communication frequency is high can be reduced.

Furthermore, the registration cancellation processing is performed onnodes where a session has been established with the mobile communicationapparatus, and therefore a disconnection of the session with thecorrespondent node due to packet loss can be prevented.

Additionally, the registration cancellation processing is performed onthe nodes where an application uses communication between the mobilecommunication apparatus and the correspondent node which becomesinoperable if there is packet loss, and therefore such an applicationcan be used even at the time of handover.

The cancellation of location registration is executed in the order ofpriority of correspondent nodes written in the BU list; therefore, whenthere is insufficient time for sending a registration cancellationmessage to all correspondent nodes, the possibility that theregistration cancellation processing can be performed on thecorrespondent nodes with high priority can be made higher.

After the mobile communication apparatus MN11 has moved to the newaccess router AR15, it is effective that the registration processing ofthe correspondent nodes in the step S809 is performed first with thecorrespondent nodes in which the registration cancellation processingflag 1105 is set to OFF. In this way, since the registrationcancellation processing has not been performed, the correspondent nodestransmitting data packets to the care-of address before movement areinformed directly of the movement destination care-of address first, andtherefore packet loss can be reduced.

In the embodiment, the access router directly performs wirelesscommunication with the mobile communication apparatus; however, theinvention is not limited to the above and it is possible that the accessrouter includes a plurality of access points or wireless base stations,and performs wireless communication with these access points or wirelessbase stations. In this case, the mobile communication apparatus realizesthe same operation and effect by the same processing.

INDUSTRIAL APPLICABILITY

As described above, this invention is effective for a mobilecommunication apparatus which moves between different subnetworks, andpreferable in performing a handover during communication with acorrespondent node to which route optimization has been appliedaccording to Mobile IPv6.

1. A mobile communication method, comprising: performing locationregistration with a home agent managing the movement of a mobilecommunication apparatus, through an access router connected to the samesubnetwork; performing the location registration with correspondentnodes; directly communicating with the correspondent nodes; detectingthe start of a handover; determining whether the access router performshandover processing using Mobile IPv6 or fast Mobile IP; and instructingthe cancellation of location registration to the correspondent nodesdirectly when the detecting step detects the start of handover, in thecase that the determining step determines that the access routerperforms handover processing using Mobile IPv6.
 2. A mobilecommunication method, comprising: performing location registration witha home agent managing the movement of a mobile communication apparatus,through an access router connected to the same subnetwork; performingthe location registration with correspondent nodes; a step that themobile communication apparatus directly communicates with thecorrespondent nodes; detecting the start of a handover; determiningwhether the access router performs handover processing using Mobile IPv6or fast Mobile IP; and instructing the cancellation of locationregistration to the correspondent nodes directly when the detecting stepdetects the start of handover, in the case that the determining stepdetermines that the access router does not perform handover processingusing a fast mobile IP.
 3. The mobile communication method according toclaim 1, wherein the mobile communication apparatus notifies all thecorrespondent nodes to which a location registration request hasperformed in the past of the cancellation of location registration. 4.The mobile communication method according to claim 1, wherein the mobilecommunication apparatus notifies the correspondent nodes which haverequested location registration in the past and which satisfy aprescribed condition in the correspondent nodes, of the cancellation oflocation registration.
 5. The mobile communication method according toclaim 4, wherein the mobile communication apparatus keeps a list inwhich addresses and other information of the correspondent nodes towhich a location registration request has been performed in the past areentered, sets a flag ordering the transmission of a registrationcancellation message to entries of the correspondent nodes which satisfythe prescribed condition, and transmits the registration cancellationmessage to the correspondent nodes whose flag is set.
 6. The mobilecommunication method according to claim 4, wherein the prescribedcondition is that the frequency of communication between the mobilecommunication apparatus and the correspondent node is high.
 7. Themobile communication method according to claim 4, wherein the prescribedcondition is that a session has been established between the mobilecommunication apparatus and the correspondent node.
 8. The mobilecommunication method according to claim 4, wherein the prescribedcondition is that the application using communication between the mobilecommunication apparatus and the correspondent node becomes inoperable ifthere is packet loss.
 9. The mobile communication method according toclaim 1, wherein the mobile communication apparatus notifies thecorrespondent nodes to which the location registration request hasperformed in the past of the cancellation of location registration, inthe order of high priority.
 10. The mobile communication methodaccording to claim 9, wherein the higher priority order corresponds tothe higher frequency of communication with the mobile communicationapparatus.
 11. The mobile communication method according to claim 4,further comprising: a step that the mobile communication apparatus givespriority to the correspondent nodes whose location registration has notbeen cancelled in advance, in notifying correspondent nodes of thelocation registration request after moving to a different subnetwork.12. A mobile communication apparatus, comprising: a registration requestpart requesting that a correspondent node make a location registration;a list storage part keeping a list of the correspondent nodes which havemade location registration; a handover detection part detecting thestart of a handover; a fast mobile IP detection part determining whethera connecting access router performs handover processing using MobileIPv6 or not; and a registration cancellation processing part directlyrequesting the cancellation of location registration of thecorrespondent nodes, and wherein when said fast mobile IP detection partdetermines that handover processing using Mobile IPv6 is performed, withreceipt of notification of the start of the handover from said handoverdetection part, said registration cancellation processing part directlyrequests the correspondent nodes in the list to cancel their locationregistration.
 13. A mobile communication apparatus, comprising: aregistration request part requesting a correspondent node to makelocation registration; a list storage part keeping a list of thecorrespondent nodes which have made location registration; a handoverdetection part detecting the start of a handover; a fast mobile IPdetection part determining whether a connecting access router performs ahandover processing using a fast mobile IP or not; and a registrationcancellation processing part directly requesting the cancellation oflocation registration of the correspondent nodes, and wherein when saidfast mobile IP detection part does not determine that the handoverprocessing using the fast mobile IP is performed, said registrationcancellation processing part directly requests the correspondent nodesin the list to cancel their location registration, upon notificationfrom said handover detection part of the start of the handover.
 14. Themobile communication apparatus according to claim 12, wherein the listis a binding update list to which registration cancellation informationis added.
 15. The mobile communication apparatus according to claim 14,wherein the list further includes priority information indicating theorder in which the registration cancellation is performed.
 16. Themobile communication apparatus according to claim 15, wherein in thelist, the correspondent nodes are listed in the order of high priority.17. The mobile communication apparatus according to claim 12, whereinthe cancellation of location registration is performed in the order ofcorrespondent nodes with higher frequency of communication with themobile communication apparatus.
 18. The mobile communication apparatusaccording to claim 12, wherein the cancellation of location registrationis performed giving priority to the nodes where a session has beenestablished with the mobile communication apparatus.
 19. The mobilecommunication apparatus according to claim 12, wherein the cancellationof location registration is performed in the case the application usingcommunication between the mobile communication apparatus and thecorrespondent node becomes inoperable if there is packet loss.
 20. Themobile communication method according to claim 2, wherein the mobilecommunication apparatus notifies all the correspondent nodes to which alocation registration request has performed in the past of thecancellation of location registration.
 21. The mobile communicationmethod according to claim 2, wherein the mobile communication apparatusnotifies the correspondent nodes which have requested locationregistration in the past and which satisfy a prescribed condition in thecorrespondent nodes, of the cancellation of location registration. 22.The mobile communication method according to claim 21, wherein themobile communication apparatus keeps a list in which addresses and otherinformation of the correspondent nodes to which a location registrationrequest has been performed in the past are entered, sets a flag orderingthe transmission of a registration cancellation message to entries ofthe correspondent nodes which satisfy the prescribed condition, andtransmits the registration cancellation message to the correspondentnodes whose flag is set.
 23. The mobile communication method accordingto claim 21, wherein the prescribed condition is that the frequency ofcommunication between the mobile communication apparatus and thecorrespondent node is high.
 24. The mobile communication methodaccording to claim 21, wherein the prescribed condition is that asession has been established between the mobile communication apparatusand the correspondent node.
 25. The mobile communication methodaccording to claim 21, wherein the prescribed condition is that theapplication using communication between the mobile communicationapparatus and the correspondent node becomes inoperable if there ispacket loss.
 26. The mobile communication method according to claim 2,wherein the mobile communication apparatus notifies the correspondentnodes to which the location registration request has performed in thepast of the cancellation of location registration, in the order of highpriority.
 27. The mobile communication method according to claim 26,wherein the higher priority order corresponds to the higher frequency ofcommunication with the mobile communication apparatus.
 28. The mobilecommunication method according to claim 21, further comprising: a stepthat the mobile communication apparatus gives priority to thecorrespondent nodes whose location registration has not been cancelledin advance, in notifying correspondent nodes of the locationregistration request after moving to a different subnetwork.
 29. Themobile communication apparatus according to claim 13, wherein the listis a binding update list to which registration cancellation informationis added.
 30. The mobile communication apparatus according to claim 29,wherein the list further includes priority information indicating theorder in which the registration cancellation is performed.
 31. Themobile communication apparatus according to claim 30, wherein in thelist, the correspondent nodes are listed in the order of high priority.32. The mobile communication apparatus according to claim 13, whereinthe cancellation of location registration is performed in the order ofcorrespondent nodes with higher frequency of communication with themobile communication apparatus.
 33. The mobile communication apparatusaccording to claim 13, wherein the cancellation of location registrationis performed giving priority to the nodes where a session has beenestablished with the mobile communication apparatus.
 34. The mobilecommunication apparatus according to claim 13, wherein the cancellationof location registration is performed in the case the application usingcommunication between the mobile communication apparatus and thecorrespondent node becomes inoperable if there is packet loss.
 35. Themobile communication method according to claim 1, wherein thedetermining step determines whether the access router performs handoverprocessing using the Mobile IPv6 or the fast Mobile IP based on a codefield in a handover capability option added to a router advertisementmessage.
 36. The mobile communication method according to claim 1,wherein the determining step determines whether the access routerperforms handover processing using the Mobile IPv6 when there is novalid response from the access router to a proxy router solicitationmessage transmitted by the mobile communication apparatus.